Self-extinguishing styrene-acrylate copolymers with brominated cycloalkyl benzene



United States Patent SELF-EXTINGUISHING STYRENE-ACRYLATE COPOLYMERS WITH BROMINATED CYCLO- ALKYL BENZENE William F. Tousignant, Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Filed Nov. 2, 1961, Ser. No. 149,500 3 Claims. (Cl. 26045.7)

This invention relates to flame retardant plastic compositions of flammable alkenyl aromatic resins. More particularly it relates to such compositions containing a combination of certain halogen-containing materials as the flame retarding agent.

By an alkenyl aromatic resin is meant a solid polymer of one or more polymerizable alkenyl aromatic compounds. Such polymer comprises in chemically combined form at least 50 percent by weight of at least one alkenyl aromatic compound having the general formula:

wherein Ar represents an aromatic hydrocarbon radical, or an aromatic halohydrocarbon radical, of the benzene series, and R is hydrogen or the methyl radical. Examples of such alkenyl aromatic resins are the solid homopolymers of styrene, alpha-methyl styrene, vinyltoluene, ar-ethylstyrene, vinylxylene, ar-chlorostyrene, ar-isopropyl styrene or ar-tert.butylstyrene; the solid copolymers of two or more of such alkenyl aromatic compounds with one another; and solid copolymers of one or more of such alkenyl aromatic compounds with minor amounts of other readily polymerizable olefinic compounds such as methyl methacrylate or acrylonitrile.

As used herein, the expressions non-flammable, flame-proof and self-extinguishing mean incapable of sustaining a flame until completely burned after a composition has been ignited in an open flame and then removed therefrom. The terms Self-extinguishing, Class I and Self-extinguishing, Class II have the meaning given them in the Underwriters Laboratories Burning Test of Plas tics, Subject 94, the differentiation between them being that Class I materials do not give rise to flaming particles or droplets during the burning test, whereas Class II materials, while self-extinguishing, do give rise to such flaming particles or droplets.

It is known that the halogen content of halogenated organic compounds, particularly of organic bromide derivatives, generally is effective to reduce the flammability of the compound itself and of flammable organic materials intimately admixed therewith. Accordingly, certain bromine containing organic compounds have been employed to render non-flammable a variety of resinous compositions. They have been used either as an intimately admixed additive for the resinous component of the nonfiammable composition or as a material copolymerizable with monomers such as styrene in the preparation of the resin.

Generally, however, the use of these materials is attended by certain difficulties. Frequently, the amount required to lend self-extinguishing properties to a given resinous composition is inordinately large and the use of the material is not economically feasible. Furthermore, the amount of a given halogenated compound required may be such that the physical properties of the resinous composition may be seriously and adversely affected. Finally, the resinous compositions incorporating these materials in an amount such that the physical properties of the compositions are reasonably maintained are ordinarily classifiable only as Self-extinguishing, Class II and are, therefore, unacceptable for a variety of applications.

As an example of the type of halogenated compounds that are reasonably effective as agents to provide selfextinguishing properties to a copolymeric compound, compounds of the following general formula may be cited,

wherein R is a hydrogen or the methyl radical, X is chlorine or bromine and m is an integer of a value of from 1 to 5 inclusive. Such compounds are readily prepared and may have a relatively large halogen content. They are copolymerizable with a wide variety of materials including the polymerizable alkenyl aromatic compounds.

A representative compound of high halogen content of the above type is 2,4,6-tribromophenyl acrylate. When this compound is copolymerized with styrene, for example, in an amount equal to about 14 percent by weight of the copolymerizable mixture, the resinous product is self-extinguishing. However, the product cannot be classified as a Self-extinguishing, Class I composition. Nor can it be raised to that classification by an increase in the amount of the 2,4,6-tribromophenyl acrylate employed; copolymers of this material and styrene remain Class II products no matter what relative amounts of the monomers are employed in their preparations.

It has now been discovered that Self-extinguishing, Class II compositions comprising alkenyl aromatic resins containing flame retardant agents of the above type can be upgraded to a Class 1 category by the addition thereto of small amounts of certain adjunctive, halogen contain ing flame retardant agents which are themselves incapable of acting alone to give Class I compositions. Specifically, it has been discovered that copolymers of alkenyl aromatic monomers and compounds of the type O antas,

wherein X is chlorine or bromine, m is an integer of from 1 to 5 inclusive, R is hydrogen or the methyl radical and R is hydrogen, the methyl radical or the group wherein X and m are as above defined may be upgraded to Class I materials by providing an intimate admixture of such copolymer with a small amount of a brominated cyclopropyl benzene of the general formula were not present the combination of chemically combined alkenyl aromatic compound and major fire retardant agent would be self-extinguishing in the Class II category.

The minor fire retardant agent is employed in a considerably smaller amount relative to the major fire retardant agent. Usually it will be present in an amount equal to from about 0.1 to about 1.3 percent by weight of the total composition.

The brominated cyclopropyl benzene that consistute the minor self-extinguishing agents may readily be prepared by the method of Dale and Swartzentruber, Journal of Organic Chemistry 24, 9557 (1959). As shown therein, the desired compounds are prepared, at a temperature of from about 10 to 5 C., of approximately equi molecular proportions of an alkali metal alkoxide, styrene or a substituted styrene and bromoforrn.

The major self-extinguishing agents of the invention are conveniently prepared, in known manner, by the esterification of the desired polyhalogenated phenol with the acid chloride of the desired unsaturated acid, as shown in application, Serial No. 142,501, of William V. Tousignant, filed October 3, 1961, now abandoned and application, Serial No. 14,502, of William F. Tousignant, filed October 3, 1961, now abandoned.

The resinous compositions contemplated by the present invention may be prepared by any of the conventional techniques employed, for example, in the preparation of polystyrene. The mixture in desired proportion of the alkenyl aromatic monomer, the major self-extinguishing monomeric agent and the minor self-extinguishing additive may thus be polymerized in mass, in aqueous suspension or in the form of an emulsion. Alternatively, the 'alkenyl aromatic monomer and the major self-extinguishing monomeric agent may be copolymerized and the resulting copolymer intimately admixed with the minor selfextinguishing additive.

The self extinguishing resinous compositions are readily fabricated into useful articles by the conventionally employed methods of compression molding, extrusion, injection molding and the like. They are possessed of excellent thermal stability and suffer little or no discoloration under the conditions of temperature obtaining in the practice of these fabrication techniques.

It may be particularly noted that the resinous compositions of the present invention exhibit their excellent self-extinguishing characteristics in the form of cellular articles equally as well as in a solid form. Thus, cellular objects of these compositions are also excellently selfextinguishing.

Cellular articles of the present compositions may be prepared by any of the known ways of preparing objects of cellular polyester. For example, they may be employed in the method of US. Patent No. 2,669,751 wherein the composition is heat-plastified in an extruder and is mixed with a normally gaseous agent such as methyl chloride or the like under superatmospheric pressure to form a gel which is brought to a temperature between about 60 and 130 C., at which temperature it remains flowable under the conditions employed, then is extruded into the atmosphere wherein the extrudate expands to form a cellular body.

The invention is illustrated by the following nonlimiting examples, wherein all parts and percentages are on a weight basis.

EXAMPLE 1 Into a glass pressure bottle there was charged a mixture of 50.4 parts of styrene, 10.0 parts of 2,4,6-tribromophenyl methacrylate, 0.5 part of (2,2-dibromo-1- methylcyclopropyl)benzene and 0.06 part of ditertiarybutyl peroxide. The air was flushed from the bottle with nitrogen. The bottle was then sealed and placed in an oil bath maintained at a temperature of 110 C. for a period of 20 hours. The resulting polymer was finely ground and devolatilized at 80 C. for 7 hours at a parts of methanol.

pressure of 1-5 mm. of mercury. Standard test bars were prepared from the polymer. These were found to be self-extinguishing in the Class I category on ignition testing.

The major self-extinguishing agent employed herein was prepared as follows:

Z,4,6-fribr0m0phenyl methacrylare Into a reaction flask fitted with a condenser, stirrer and dropping funnel there was charged a mixture of 2317 parts of 2,4,6-tribromophenol, 707 parts of triethylamine and 5320 parts of methylene chloride. From the dropping funnel there was added, with stirring, 728 parts of methacryloyl chloride during 1 hour. At the conclusion of this addition, the reaction mixture was maintained at the reflux temperature of 40 C. for an additional 4 hours.

The reaction mixture was freed from the triethylamine hydrochloride by-product and unreacted 2,4,6-tribromophenol by thorough and successive washings with water, dilute caustic soda solution, dilute hydrochloric acid and water.

To the methylene chloride solution of reaction there was added a mixture of 2000 parts of water and 1000 The methylene chloride was distilled from the mixture under a moderate vacuum at about 30 C. A crystalline product was obtained when removal of the methylene chloride was substantially complete. The crystalline product was filtered, washed and dried. There were obtained 2367 parts of white, crystalline 2,4,6- tribrornophenyl methacrylate, M.P. 6263 C.

EXAMPLE 2 The preparation described in Example 1 was repeated with a monomer charge in which the (2,2-dibromo-l methylcyclopropyl)benzene was omitted. Standard test bars prepared from the resulting polymer were found to be self-extinguishing in the Class II category.

EXAMPLE 3 EXAMPLE 4 According to the method of Example 1, copolymers were prepared in which (2,2-dibromo-l-cyclopropyl)- benzene replaced the (2,2-dibr omo-1-methylcyclopropyl)- benzene of that example. The composition of representative Class I Self-Extinguishing compositions is set out in Table I, below.

TABLE I 2,4,6-tribrom0phenyl (2,2-dibrom0-cyclo- Styrene, Percent methaerylate, Percent propyl) benzene Percent What is claimed is:

1. A non-flammable thermoplastic polymeric composition comprising an intimate admixture of from about 0.1 to about 1.3 percent by weight of a compound (A) selected from the class consisting of (2,2-dibromocyclopropyl)benzene and 2,2-dibromo-1-methylcyclopropyl)- benzene and a polymeric composition (B) comprising in chemically combined form (1) from 79.7 to 92.9 percent by Weight of at least one alkenyl aromatic compound having the general formula Ar-CH=OH wherein Ar represents an aromatic hydrocarbon radical and (2) from about 7 to about 19 percent by weight of a compound of the general formula wherein m is an integer from 3 to 5 and R is a member of the group consisting of hydrogen and the methyl radical all weight percentages being based on the total weight of the non-flammable thermoplastic polymeric composition.

2. A composition according to claim 1 wherein the compound A is (2,2-dibron1ocyclopropyl)benzene.

3. A composition according to claim 1 wherein the compound A is (2,2-dibrorno-l-methylcyclopropyDben- 5 zene.

References Cited by the Examiner UNITED STATES PATENTS 10 3,044,999 7/62 Tousignant 260'--86.3 X

FOREIGN PATENTS 558,943 6/58 Canada.

LEON J. BERCOVITZ, Primary Examiner. ALPHONSO D. SULLIVAN, Examiner. 

1. A NON-FLAMMABLE THERMOPLASTIC POLYMERIC COMPOSITION COMPRISING AN INTIMATE ADMIXTURE OF FROM ABOUT 0.1 TO ABOUT 1.3 PERCENT BY WEIGHT OF A COMPOUND (A) SELECTED FROM THE CLASS CONSISTING OF (2,2-DIBROMOCYCLOPROPYL)BENZENE AND (2,2-DIBROMO-1-METHYLCYCLOPROPYL)BENZENE AND A POLYMERIC COMPOSITION (B) COMPRISING IN BY WEIGHT OF AT LEAST ONE ALKENYL AROMATIC COMPOUND HAVING THE GENERAL FORMULA 